Flow operated machinery, such as gas turbines, are typically designed for a particular operational condition which will be most frequently encountered in the environment where that particular machine will be utilized. In that situation, operation of the machine under the design condition will produce optimum proficiency. As a practical matter, however, it is often necessary to operate such machines under conditions which vary substantially from the optimum design parameters. This particularly occurs during part load operation of a turbine, where gas throughputs are considerably less than those encountered under optimum operating conditions. This obviously causes a reduction in the efficiency of the turbine and instabilities in the operation of the machine.
Several attempts have been made in the prior art to control the effective flow area of gases flowing to the turbine rotors of a gas turbine engine. In one such structure, rotation of the vanes was utilized to change the flow area, but this also changes the flow angle of the air flow impinging on the turbine rotors. Another prior art approach involves the use of an end wall which was movable in the axial direction to achieve a reduction in the cross-sectional flow area. Both of these prior art attempts to achieve flow area changes require the use of fairly elaborate mechanical apparatus which has presented sealing and cooling problems, and which detracts from any gain in efficiency achieved by the variable flow area feature.
A technique for varying the flow pattern in a turbine machine is disclosed in U.S. Pat. No. 3,643,675 to Wetterstad. The Wetterstad patent describes an apparatus for controlling the velocity profile of a working medium in a turbine, including a plurality of conduits radially disposed in an inlet of the turbine for introducing or injecting a control medium tangentially into the working fluid of the turbine. The control fluid imparts a rotational motion to the working fluid. The flow path of the working fluid also includes a restriction for reducing the cross-sectional area of the flow path of the working fluid to amplify the rotational motion of the fluid. This prior approach was specifically intended to eliminate the use of guide vanes which are considered by Wetterstad to be complicated and expensive, and which are said to give rise to flow losses.
Although this prior art approach does allow for variation of the velocity profile of the turbine gases, it has not proven to be effective in practice, and has not been adopted commercially.
Accordingly, it is a primary object of this invention to improve the operational efficiency of a gas turbine engine.
It is a further object of this invention to vary the effective flow area of gases flowing from the combustors of gas turbine engine to the turbine rotors thereof.
Yet another object of the invention is to efficiently operate a gas turbine engine under varying loads and flow regimes.
Additional objects and advantages will be set forth in part in the description which follows, and in part, will be obvious from the description, or may be learned by practice of the invention.